The present invention relates to equipment and machinery for providing smooth wall tubes with helical corrugation. The invention will find particular utility for corrugating tubes which were made originally by longitudinally folding metal strip and longitudinally welding the butting edges; however, the invention is not limited to corrugating that kind of tubing.
Equipment for corrugating smooth walled tubing is comprised, for example, of a corrugating head which can rotate about an axis in a fixed stand. The head includes, particularly, an annular tool moving at the same rotational speed as a corrugating head and having an opening to be traversed by the longitudinally advancing tube to be corrugated. The particular annular tool has, on its inside, a helical working and deforming edge whose smallest diameter is smaller than the outer diameter of the smooth wall tube passing through. The invention, in particular, relates to improvements of equipment of that type.
Other equipment is known for making corrugated tubing whereby in particular two methods or types of methods have become known for obtaining the corrugation. In accordance with a first method, a corrugating tool (roller) rolls on the tube and around the tube to provide thereby a continuous helical corrugation. This method can be considered rather elegant due to the point by point deforming of the smooth wall tube to obtain the corrugation. Moreover, this particular method exhibits very little friction heating and is, therefore, quite suitable for high speed operation. However, it was found that this particular method has a disadvantage in that the point by point formation introduces irregularities in the metal strip as well as in the seam and this may even lead to local detents other than corrugation grooves. It was also found that the distance in axial direction from corrugation ridge to corrugation ridge will not remain constant, for example, due to differences in hardness and strength of the strip material. The invention does not relate to that type of method.
In accordance with a second corrugating method, a particular tool having a single threading is screwed onto the tube to obtain a helical corrugation. This method permits, indeed, the production of a constant corrugation pattern as far as the axial ridge-to-ridge or even peak-to-peak distance of the corrugation is concerned. It was particularly found that for making high frequency cable, this method is quite suitable for exactly that reason (see German printed Pat. application 2,049,235).
In cases, it is desirable to provide corrugating metal tubing in which the corrugation pitch varies. This requirement may exist, for example, in corrugated tubes for high frequency cable and, in particularly, for purposes of employment as a wave guide or in a coaxially type of HF conductor having a corrugated inner conductor and separate corrugated outer conductor.